Electrical protective device.



B. H. SMITH.

ELECIRICAL PROTECTIVE DEVICE. APPLICATION mm was. ms.

1,241,571. Patented Oct. 2,1917.

35 39 mum: 36 llllmlmk w I M M F WITNESSES I INVENTOR Aim 4mm 15. Jar/2% BY O-dT/ ATTORNEY ers that UNITED STATES PATENT OFFICE.

BENJAMIN E. SMITH, OF TURTLE CREEK, PENNSYLVANIA, A S SIGNOB TO WESTING- HOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIA.

ELECTRIOAL PROTECTIVE DEVICE.

Specification of Letters Patent;

Patented Oct. 2, 1917.

Application filed August 6, 1915. SerialNo. 43,975.

electric circuits that will operate without vibration when relatively large overloads traverse the circuits.

In the usual watt relays heretofore employed for trippin circuit interrupters, upon the reversal 0 the power traversing the circuit, considerable difficulty was encountered at relatively large overloads. This diificulty consisted in the vibration of the contact members which caused ineifective engagement between them.

I provide means for limiting the current that is supplied to the current coils of the watt relay to thus reduce the vibration, and I further provide means whereby the correct hase relation between the currents traversmg the potential and current windings of the relay is maintained.

In order to accomplish the above indicated results, I rovide relatively small transformecome magnetically saturated at predetermined loads, and I connect these transformers between the current windings of the rela s and the circuit. However, at relatively igh currents in the circuit, the phase angle of the current traversing. the

current windings will shift ahead a consid-' erable amount, and the diflI'erence in phase relation between the current traversing the potential and the current windings will be of such value that, whenever there is a singlephase short circuit, the relays will not operate correctly. In order to overcome this difficulty, I connect the current windings in star relation to the circuit and the potential winding in delta relation. By such connections, the current traversing the potential windings is advanced substantially 30 ahead of the current traversing the current windings, under normal conditions. Thus, when the phase an le of the current traversing the current win ing shifts forward because of the saturation of the relatively small trans formers, there still be suflicient angular diflerence between the phases .of the ,cur-

rents in the two windings to. efi'ect correct operation.

The singlefigure of the accompanying drawings illustrates an electrical circuitthat is protected by relays embodying myinvention. i

A polyphase electric circuit 1 comprises ,three conductors 2, 3 and 4.. The conductors 2, 3 and 4 are provided with circuit interrupters 5, 6 and 7 and with current transformers 8 9 and 10, respectively, the primary windings 11,.12 and '13 of which are connected in circuit with the conductors 2, 3 and 4, respectively. In order to trip the circuit interrupters 5, 6 and 7, upon the re versal of, energyin circuit 1, I provide three watt relays 14, 15 and 16,

The watt relays 14, 15 and 16 comprise magnetizable core members 17, 18 and 19, current windings 20, 21 and 22, potential windings 23, 24 and 25 and rotatable arrnatures 26, 27 and 28 to which are operatively. connected contact members 29, 30 and 31, respectivel The circuit interrupters 5, 6 and 7 are provided with trip coils 32, 33 and 34, respectively, each of which is operatively connected to a source of electromotive force 35 to constitute trippin circuits 36, 37 and 38. The contact mem ers 29, 30,and 31 cooperate with stationary contaot members 39, 40 and 41 to constitute the separable terminals of the circuits 36, 37 and 38, respectively. a Three relatively small transformers 42, 43.and 44, the core members of which are adaptedto become magnetically saturated under predetermined conditions, have their secondary windings 45, 46 and 47 operativel connected in circuit with the current win ings 20, 21 and 22, respectively. The primary windings 48, 49 and 50 of the transformers are connected in circuit with the secondary windings 51, 52 and 53 of the transformers 8, 9 and 10. The wmdings 51, 52 and 53 are connected in star relation to the windings 11, 12 and 13. The primary windings 54 and 55 of two potential transformers 56,and 57 are connected to the cir cuit 1, and the secondary wmdmgs 58 and 59 thereof are connected to the potential windings 23, 24 and 25. From the foregoing, it will be understood that the current windings are star connected to the circuit 1 and the potential windings are delta connected tothe circuit 1, whereby the current tifiie sing the potential winding ,is shifted substantially 36 ahead of the normal current traversing the circuitil.

If the potential windings 23, 24 and 25 are-connected gin star ,and the saturatable transformers 42, 43 and 44 are used to preclude an excessive current to 'traverse the windings 20, 21 and 22, .the phase-angular relation between the currents traversing the current and potential windings of the relays wince-under some conditions, greater than ninety degrees. This will causethe relays -to fluictionjimproperly because it will not "indicate amen-Sn of the current in the defective incultf However, if the potential windin 23, 24 .and 25 are connected in delta, -e currenttraversin the same is adegrees ahead of the current traversing t respective current windin under normal conditions. "Thusfwhen t e phase angle of the current 'traversin the current windings shifts forward'at" igli loads because oi the saturatable itransforr'hers, the phase-angular relation between thejcurrents traversing the current and potentialwindings will not exceed ninety degrees and the relays will function p p yr "Whena relatively large amount of energy traverses the'circuit 1 1n the reverse direction t e windings 20, 21 and '22 will be energ'ize 'byhxlbstantmlly constant current, and thepotential windingswillbe energized b current that is proportional to the potentiiil oftlre circuit and havinga phase angle that is substantially 30 ahead of the ,phase angle of the normal current that traverses the circuit 1. The currentstraversing the current and potential windings cooperate to cause the armatures26, 27 and 28 to turn and the contact members29, '30 and '31 to engage the stationary contact members 39, 40 and 41, respectively, to thereby trip the circuit interrupters 5, 6 and 7.

It i's understood 'that my invention is not limited to the particular devices illustrated, butis capable of various modifications within "the spirit and scope of the appended claims.

- I claim as my invention:

1. In a polyphase electric circuit, the com- 'bination with circuit interrupters and relays for controlling the trippin of thesaid interrupters, of, saturatedtran ormers that are starconnected to the circuit for supplying current to the ,currentwindings of the watt relays, the potential windings of the relays being delta connected to the circuit.

2. In a polyphase electric circuit, thecomhii-iation with circuit interruptersand relays for controlling the tripping of thesaid internipters, of-s'tar-connected means lfor sup- ,reverse-"energ plying-the current windings of the relays with substantially constant current, and means {or soconnecting thepotential windrings of :the relays to the circuit that the phase-angular relation between the ;currents vtraversingthe windings of the respective relays will be less than ninety degrees.

-ln a-polyphasc electric circuit, the combination with circuit interrupter-s and relays for controlling the tripping thereof, of means for supplying the current windings of the relays with substantially constant current, said means'beingstar connected to 'the circuit, the potential windings ofthe relays being delta connected to the circuit.

'4. Ina polyphasc electric circuit, the combination with watt "relays having [current be substantially constant above a predetermined ralue, the potential winding being so connected to thecirc ui't'that the current that traverses thepotentlal windings is a predetermined angle out of phase with the current that traverses the current windings.

"6. In a polyphase electric circuit, the combination with watt relays having current and potential windings thereon, of means operativcly connected between the current windings and the circuit for causing the currentthat traverses the current windings to be substantially constant above a predetermined va'lue, the potential winding being so connected tothe circuit that the current'that traverses the potential windings is thirty degrees out of phase with the current that normally traverses the circuit.

7. 'In a three-phase electric circuit, the combination with circuit interrupters and relays for controlling the tripping of t e said interrupters, of means for-so controlling the currentthat traverses the current windings of the relays that they do not vibrate when excessive currents traverse=-the circuit.

8. In a three phase electric circuit, the combination with circuit interru ters and watt relays for controlling the tripping of the said interrupters, of means for so cantrollingthe current that traverses the current windings of the'relaystha't they do not vibratewhen excessive currents traverse the circuit, the current and potential windings of the relays being so connected to the circuit that the currents traversing the same are maintained in predetermined phase relationship.

9. In a three-phase electric circuit, the combination with circuit interrupters and watt relays for controlling the tripping of the said interrupters, of means for so controlling the current that traverses the current windings of the relays that the movable members thereof do not vibrate when excessive currents traverse the circuit, the current and potential windings of the relays being so connected to the circuit that the current which traverses the potential winding is thirty degrees ahead of the current that normally traverses the circuit.

In testimony whereof, I have hereunto subscribed my name this 30th day of July 1915.

BENJAMIN H. SMITH.

Copies of this patent may be obtained for five cents each, by addressing the Gommissloner of Patents, Washington, D. G. 

